virtual wifi: bring virtualization from wired to wireless

Virtual WiFi: Bring Virtualization Virtual WiFi: Bring Virtualization from Wired to Wireless

Lei Xia, Sanjay Kumar, Xue Yang

Praveen Gopalakrishnan, York Liu,

S b ti S h b Xi GSebastian Schoenberg, Xingang Guo

Northwestern University EECSNorthwestern University, EECS

Intel Labs, Hillsboro, OR

This work was done in Intel Labs during Xia’s internship th

Virtual WiFi

• New virtualization approach suitable for i l LAN i t li tiwireless LAN virtualization

• Full wireless LAN functionalities are supported inside VMsMultiple separate wireless LAN connections are supported • Multiple separate wireless LAN connections are supported through one physical wireless LAN network interface

Wireless VirtualizationWireless driver stack sits in Host OS onlyVMs see only wired NIC

Wireless driver stack runs inside the Guest as well

Wireless functionality invisible to Guest

Providing rich wireless functionalities to Guest

Wireless Driver

Wireless ProfileGuest OS

Wireless Driver


Ethernet Driver


Ethernet Driver


VMMWireless MultiplexingWireless Multiplexing

Host OS

VMMEthernet EmulationEthernet Emulation

Host OS

VMM

Virtualization Augmented Wireless Driver

VMM

Wireless Device Driver

VVirtualization enabledWireless NICWireless NIC

Today Virtual WiFiToday Virtual WiFi

Why we need virtual WiFi?y

• Client Virtualization

• Enterprise IT: Separate enterprise & personal applications, data and configurations

User ITUser VM

ITVM

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Company PrivateNetwork

Guest Network

Why we need virtual WiFi?y

• Mobile and ultra-mobile devicesMobile and ultra mobile devices• Separate work from play• User connect exclusively through wirelessUser connect exclusively through wireless• Software tools depend on WiFi connectivity

• WiFi-based Location-Aware SystemWiFi based Location Aware System• Maps WiFi hotspots to determine location

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Wireless LAN Specific Features

• Complex management functions that affect the functionalities of WLAN devicesfunctionalities of WLAN devices.

• Scan/Associate to specific access pointR t d ti• Rate adaption

• Dynamic switching data rates to match the channel conditionsconditions

• Power management• Device driver can control how long and how often the g

radio needs to be on to save battery

• ……

• Device driver has to be involved in many of those management decisions

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Required Hardware Support

• Multiple virtual MACs in wireless NICA il bl f i l WiFi d i F • Available on most of commercial WiFi devices, For example, used in Intel MyWiFi technology

i l i i d h h l• Virtual WiFi extends such technology• To support wireless virtualization, multiple MAC entities maintain their independent associations with maintain their independent associations with corresponding APs

• Number of independent associations dependent on number of vMACsnumber of vMACs

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Virtual WiFi: System Architecturey

Virtual WiFi: Architecture

• VMs run native Intel WiFi device driverUsing WiFi features from device driver• Using WiFi features from device driver

• Guest manage its own WiFi connections

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• VMs run native Intel WiFi device driver

d l l• Device Model exposes same virtual WiFi device to VM as physical device

• Commands from guest can be pass to physical device without translation

f• Device model (VMM) knows few about device-specific knowledgeWi l d i i ll d d t f VMM • Wireless vendor minimally dependent of VMM vendor

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Virtual WiFi: Architecture• VMs run native Intel WiFi device driver

• Expose same virtual WiFi device to VM as physical device

• Virtualization Augmented host Wireless device driver device driver

• Management functions of virtualized wireless interfaces

• Logically assigns vMAC to a VM• Processing commands from device model

• Forwarding them directly or with consolidation or• Emulated some locally

• Forwarding receive network packet to VMs• Mapping table between vMAC and VM

Configuration/connection status/state machine for

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• Configuration/connection status/state machine for each vMAC/VM pair


• Address Translation• Commands from guest: GPA->HPACommands from guest: GPA >HPA

• Avoids extra memory copy for TX packets• Either Software/Hardware IOMMU• Either Software/Hardware IOMMU• Enable VT-d table to support multi-domain for

single devicesingle device• Collapse multiple page tables to single

address translation table in VT-d

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Augmented Host Device Driver Commands HandlingHandling

• TX command• Pass it directly to associated vMAC on WiFi NIC

• Rate Control Command• Only update the rate table associated with the specific VM-

ID

• Device Initialization• Start a new vMAC, and starting state/information mapping

to new vMAC

• Scan request• Consolidate properly of scan requests from different VMs• May return previous stored scan results to VMs

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• And a lot more ……

Performance• Benchmarks

• Chariot benchmark tool• Metrics: TCP & UDP throughputs, • Ping round-trip latency

• Setup• HP EliteBook 6930p Laptop with Intel Core2 Duo CPU

2 53GH ( d) 4GB RAM 80GB HD2.53GHz (one core used), 4GB RAM, 80GB HD• Intel WiFi 5300 AGN Card + Cisco WAP410N AP• KVM + Qemu + Linux 2 6 33 1KVM + Qemu + Linux 2.6.33.1

• Comparing GroupsVirtual WiFi: VM with virtual WiFi system• Virtual WiFi: VM with virtual WiFi system

• Native: Linux with Native WiFi driver• Passthrough: VM with direct assigned WiFi devicePassthrough: VM with direct assigned WiFi device

Performance – TCP Throughputs

20

15

s

10

Mbp

s TX

RX

5

0

Native Passthrough Virtual WiFi

Performance - UDP Throughputs

20

15

bps

TX

10M RX

0

5

0Native Passthrough Virtual WiFi

Virtual WiFi: Performance - Latency

8

6

s

4ms

2

0Native Passthrough Virtual WiFi Virtual WiFi(VT‐d)

VM Additional Latency on TX-path

Host DriverGpa->Hpa

60,000 Gpa >HpaUser/Kernel SwitchDevice Model

40,000

Cyc

les Kernel/User Switch

KVM HandlingAddress translation takes

CPU

C Address translation takes almost half of the time

20,000

0

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Software VT-d

System Overall CPU Cost( i l 2 53GH )(single core, 2.53GHz)

60.0

50.4 50.0

40.0

23.1

19.3 20 0

30.0

CPU %

9.9 10.0

20.0

4.8

0.0

Virtual WiFi Passthrough Native VM‐Idle System‐Idle

Major Virtualization Overheads

• Address translationAddress translation• Solution: Hardware IOMMU

• IOMMU hw do the address translationIOMMU hw do the address translation• Reduce the VM additional latency/CPU usage

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• Interrupt Handling • Coalesce interrupts disabled in host device driver• Each physical interrupt leads to more

synchronization & signal VMs and kernel• Solution: Interrupt coalescing in device model

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• Interrupt Handling • Solution: Interrupt coalescing in device model

• I/O handling • MMIO handling• MMIO handling

•Context switches, Threads synchronization overhead for each TX/RX packetoverhead for each TX/RX packet

• Solution: Fast data pass-through (Future Work)• Data traffic passthrough into physical device through • Data traffic passthrough into physical device through

separate queueIntel Confidential

CPU Usage with Optimizations

Virtual WiFi consumed 9% more CPU h i

60CPU than native

50

40

%

30

CP

U

%

0

20

C

0

10

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0Original Coalese HW IOMMU Coalese+hw

IOMMUNative

Related Work

• MultiNet (Microsoft vWiFi)A f l h b h i l LAN d • A software layer that abstracts the wireless LAN card hardware into multiple virtual adapters

• Continuously switch the wireless card across multiple wireless Co uous y s c e e ess ca d ac oss u p e e essnetworks

• Virtual Pass-through IO (VPIO)• A modeling-based approach to high performance I/O

i t li tivirtualization• Device is directly assigned to guest• Most of IOs from a guest are directly applied on physical Most of IOs from a guest are directly applied on physical

device, no VMM inventions. • VMM uses a behavior model to determine when IO has to be

i t t d f it d d i it hiintercepted for security and device switching

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Summary• Virtual WiFi: new virtualization approach for

wireless LAN device• Support fully wireless functionalities inside VMs• Separate wireless connections among VMs through

one ph si al i eless inte fa eone physical wireless interface

• Prototype system using virtual WiFi• Native throughputs with 7% extra latency• Less than 9% more CPU cost

Lei Xia Ph.D candidate, Northwestern University

http://www.cs.northwestern.edu/~lxi990

http://v3vee.org

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Backup SlidesBackup Slides

Backup Slides

Backup SlidesBackup Slides

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Current Wireless virtualization

• Map network connections to virtual wired Map network connections to virtual wired Ethernet device

W k ll f d t t f• Works well for data transfer

• But downsides for wireless connectionu do d o o o

• Feature of network infrastructure can not be controlled from inside VMnot be controlled from inside VM

• Wireless NIC has to be configured and gmanaged by VMM

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System profiling setup

• Profiling Components for virtual WiFi systemProfiling Components for virtual WiFi system• Kernel: App-specific, kernel-general

Kernel modules: KVM driver• Kernel modules: KVM, driver• Application-level: Endpoint, Qemu, Guest

• Presented test results based on KVM/QEMU; Presented test results based on KVM/QEMU; similar evaluations need to be performed for other VMM software, such as Xen.for other VMM software, such as Xen.

Comparing Groups

Native:

Endpoint

Native:Linux with

native driver

Host Linux Kernel

Endpoint

WiFi Driver

Kernel

WiFi Device

(Original Driver)

WiFi Device

Comparing Groups

Qemu

Endpoint

Guest OS

Device Model

WiFi DriverVirtual WiFi

Endpoint

Host Linux Kernel

KVM

Device Model

WiFi Driver

Kernel

WiFi Device

(Augmented Driver)

WiFi Device

Comparing Groups

Qemu Guest OS

WiFi DriverPassthrough

Endpoint

Host Linux Kernel

irtual WiFi Device MoKVMirtual WiFi Device Mo

WiFi Device

Virtual WiFi: Implementation

Qemu Guest OS

Virtual WiFi

Native WiFi Driver

A li ti

Host Kernel

KVM

Device ModelApplication

Augmented WiFi Driver

KVM

WiFi Device µCode

• Type II hosted VMM

C b il d T I b • Can be easily ported to Type I bare metal VMM

Implementation

• Virtual WiFi Device Model• Expose only PCI config and MMIO mapping• Tag command with VM-ID, Injecting virtual interrupt to

VMsVMs.

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Implementation

• Virtual WiFi Device Model

• Augmented WiFi Device driver• Forwarding commands directly to physical WiFi g y p y

device, or Emulated some locally• Receive network packet from WiFi interface,

Identify destination VM, signal device model

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Implementation

• Vdel

• Augmented WiFi Device driver

Augmented NIC• Augmented NIC• Only uCode update needed

l dd d d• Virtualization extension added to uCode

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The CPU Usage Matters!

• ScalabilityScalability• From 802.11g (50Mbps) to 802.11n (up to

500Mbps)p )• CPU usage grows with throughput

M bil l tf• Mobile platform• Limited processor resources

• User experience

CPU Usage breakdown (Chariot TX)

• Virtualization directed overhead: Guest, Qemu and KVM overhead (20%)

60 Chariot

• VM Kernel consumes more than Native case (9%)

Guest

Qemu

k• VM-PT needs very few KVM and Kernel involvement

40

%

kvm

Kernel-App

Kernel-General

CP

U Kernel-General

driver

20

0

vWiFi Passthrough Native VM-Idle System-Idle

CPU Usage breakdown:KVM and Host Kernel (by Oprofile)( y p )

Future Works

• Data Pass-through• Data traffic passthrough into physical device

through separate queue• Control/management commands go through device

model/augmented driver

• Apply on next generation WiFi standards• WiFi 802.11nWiFi 802.11n• Expected throughput: ~500Mbps

Related Work

• Full-virtualization by emulating– Large performance overhead, Many development efforts,

Lack of device datasheets

• Para-virtualization• Need guest modification/new para-virtualized device driver• WLAN device specific features are closed to VMM vendor for

back-end driver

• SR-IOV: hardware support virtualization• Costly/complexity/Time line

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virtual wifi: bring virtualization from wired to wireless

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